1. Technical Field
The present disclosure relates to a display device, and in particular, to a display device capable of controlling an external light and a control method thereof.
2. Related Art
With the advantages of being light, thin, and large-sized, liquid crystal televisions (TVs) and plasma display panel (PDP) TVs already become first choices of television purchasers. An important factor of specifications in selecting TVs or displays is contrast ratio. The contrast ratio refers to a quotient of dividing brightness of white color divided by brightness of black color of a display. A higher contrast ratio means that the display exhibits a clearer distinction between white color and black color, thereby obtaining a better picture quality and a better sense of color level. Therefore, a higher contrast ratio is always pursued by manufacturers in the display industry.
At present, a contrast ratio of the display is measured in a darkroom where brightness of ambient light is lower than 1 lux. However, such definition does not entirely adapt to practical situations. A major reason is that, in actual use, there is usually an environmental light around the display, but the contrast ratio is not measured in a situation having the environmental light. When watching TV, people usually turn on all indoor lights to maintain a bright environment. Therefore, it is not enough to just take the contrast ratio measured in the darkroom as a reference factor for evaluating performance of the display. Instead, what is really seen by human eyes is a visual effect accompanying another contrast ratio which contains an additive contribution from the brightness of external lights in a bright room.
Since the contrast ratio is defined as the quotient of dividing the brightness of white color by the brightness of black color of a display, the contrast ratio may be increased by increasing the brightness of a white image or decreasing the brightness of a black image. However, increase of the brightness of the white image cannot be achieved to a great extent in one aspect due to limitations of current backlight technologies and materials of optical modules related to light guiding, and in another aspect increase of the brightness results in larger power consumption of backlight modules. On the other hand, it is more effective to decrease the brightness of the black image. For example, if originally the brightness of the white image and the brightness of the black image of a display are respectively 500 nits and 1 nit, the contrast ratio is 500 nits/1 nit=500. If the brightness of the white image is increased to 600 nits, the contrast ratio can be increased to 600 nits/1 nit=600. If the brightness of the black image is decreased to 0.5 nit, the contrast ratio can be substantially increased to 500 nits/0.5 nit=1000.
Although dynamic contrast technologies may be used to solve contrast related problems, cost of the display device would be increased, and the contrast ratio is still affected by the external lights. Therefore, in consideration of influence of the environmental light on the display device in an actual use environment, it is desired to develop a technology which improves contrast effect of the display without largely increasing the cost.